Are HOF diamonds graded by the GIA? Or another grading laboratory?

Yes, all of the Hearts On Fire diamonds are graded by the AGS lab, which has a higher standard of grading than the GIA. The difference between the two is that the GIA focuses more on the color quality whereas the AGS focuses more on the cut of the diamond. The AGS has a stricter guideline for how it grades its diamonds, and since we concentrate on how the cut of the diamonds creates value, we choose to work with the AGS.